1. Field of the Invention
This invention relates to multi-band antenna, and more particularly to a built-in multi-band mobile phone antenna.
2. Description of the Related Art
Advancements in electronic communication technology have led to a reduction in the overall sizes of mobile phones, personal digital assistants (PDA), and the like. Built-in type mobile phone antennas are attractive accordingly, and include planar inverted F antennas (PIFA), microstrip antennas, etc.
Referring to FIG. 1, a conventional PIFA 5 is shown to include a conductive flat radiating plate 51 that defines a gap 52 and that has a first plate portion 511, a second plate portion 512, a signal feeding point (F) that is disposed between the first and second plate portions 511, 512, and a grounding point (G) that is adjacent to the signal feeding point (F). The radiating plate 51 is connected electrically to a coaxial cable 54 at the signal feeding point (F), and to a grounding plate 6 at the grounding point (G) via a conductive grounding leg 55. Four dielectric legs 56 are fixed on the grounding plate 6 for supporting four corners of the radiating plate 51. The conventional PIFA can operate in a 900 MHZ frequency band and a 1900 MHZ frequency band so that the bandwidth of the PIFA is relatively narrow, thereby resulting in poor signal communications. A parasitic element 7 (see FIG. 2) can be added to the PIFA so as to widen the bandwidth of the 1800 MHZ frequency band, thereby facilitating the signal communications. However, the bandwidth of the 900 MHZ frequency band still cannot be widened.
The object of this invention is to provide a compact built-in multi-band mobile phone antenna, which can overcome the drawbacks associated with the prior art.
According to this invention, a built-in multi-band mobile phone antenna includes: a meandering conductive body having a signal feeding point, and first and second meandering conductive portions disposed at two sides of the signal feedingpoint; a conductive flat first radiating plate in electrical connection with the first meandering conductive portion and tuned to a low frequency range; an elongated conductive flat second radiating plate in electrical connection with the second meandering conductive portion and a grounding point and tuned to a high frequency range; and a conductive flat parasitic plate in electrical connection with the grounding point so as to widen the bandwidth of the antenna. The conductive body, the first and second radiating plates, and the parasitic plate define cooperatively a plate-shaped accommodating space thereamong for receiving a plate-shaped electronic element, e.g. a printed circuit board.
The low frequency range includes a 900 MHZ frequency band corresponding to a GSM frequency band, the bandwidth of which is widened by the parasitic plate. The high frequency range includes a 1800 MHZ frequency band corresponding to a DCS frequency band, and a 1900 MHZ frequency band corresponding to a PCS frequency band because the first and second meandering conductive portions can widen the bandwidth of the 1800 MHZ frequency band so as to transmit and receive a 1900 MHZ frequency signal.